The present invention relates in general to electrically conducting components and more particularly to automotive and appliance type protective fuses which have a fusible link element encapsulated in a thermoplastic material.
In the U.S. Pat. No. 3,832,664 issued to the inventor of the present invention, a fuse is disclosed in which an elongate wire-like fusible link element is disposed within a generally cylindrical thermoplastic body having oppositely facing body ends. End portions of the wire-like fusible element extend outwardly beyond the ends of the body and are bent over at an angle so that they lie generally adjacent and parallel to the body ends. Generally cup-shaped end caps are positioned on the fuse body and the angled end portions of the wire-like fusible element are compressed between the opposed end surfaces of the fuse body and the end walls of the end caps. This provides a positive electrical connection between the wire-like element.
Electrical conducting components for fuses having a structure similar to that disclosed in the above-described U.S. Pat. No. 3,832,664 offer a number of advantages of structure and of ease of manufacture. However, with certain methods of manufacture, involving certain types of fabricating apparatus operated at very high speeds on a production line basis, it is possible to force the end caps against the fuse body ends with an excessive amount of force so that the bent over portions of the wire-like element are pushed against the fuse body ends with an undesirably high amount of force which can cause the wire-like element end portions to be severed from the main portion of the element embedded in the thermoplastic body. Obviously, such severance can partially or totally destroy the electrically conductive path between the end caps.
It would be desirable to provide an electrically conducting component which would offer the many advantages, including simplicity and ease of manufacture, of the fuse disclosed in the above-described U.S. Pat. No. 3,832,664. It would be desirable to provide a structure which would allow manufacture of an electric conducting component using electrically conducting end caps which could be manufactured using very high speed end cap applying apparatus so that the possibility of severing the bent over wire-like fusible link or other conducting element end portions upon application of the end caps is substantially reduced or totally elminated.
Though the fuses of the type disclosed in the above-described U.S. Pat. No. 3,832,664 function well, and as intended, when properly made in accordance with the teachings of the specification of that patent, with certain high speed manufacturing processes and with certain high speed apparatus used to effect such manufacturing processes. It is possible that the end caps may not always be applied to the fuse body ends to achieve the positive electrical connection structure disclosed in the patent. Specifically if the end caps are not fully inserted onto the fuse body ends, the bent over end portions of the wire-like element may engage the end wall of the end caps at only one point, or at only a few points, of contact. This may result in very poor electrical conductivity between the end caps and the wire-like fusible element.
With certain types of high speed end cap applying apparatus, the end caps are first initially moved axially against the fuse body ends to bend the end portions of the wire-like element toward or against the fuse body ends. Subsequently, the end caps may be crimped onto the fuse body and the apparatus is withdrawn while the end caps remain on the fuse body ends. If the high speed end cap applying apparatus is not functioning properly, or under certain impact rebound conditions, the end caps, after being moved onto the fuse body ends by the apparatus, may be accidentally pulled some amount outwardly from complete engagement with the fuse body ends. An end cap may be pulled out a sufficient amount so that there is no longer any electrical contact between the bent over end portion of the wire-like element and the end wall of the end cap. In such cases, there will be no electrically conducting path between the two opposed end caps on the fuse body.
It would be desirable to provide an end cap structure which would allow the placement of an electrically conductive fluid material within the end cap structure and surrounding bent over end portion of a wire-like element so that the electrical conductance between the end cap and the wire-like element would be improved and so that, even if the bent over end portion was not in direct physical contact with the end wall of the end cap, electrical conduction would be possible between the end cap and the element by virtue of the electrically conducting material filling the voids between the element end portion and the end cap.
One of the important design characteristics of an electrically conducting component, including fuses, is the internal resistance of that component. In many cases, it is desirable that the internal resistance be either as low as possible or maintained at some specific, predetermined amount. With electrically conducting components which have internal connections, the total internal resistance of that component includes the so-called contact resistances which are present at each internal connection or contact point. In order to reduce contact resistances, it is generally desirable to provide a component that has very low internal contact resistances. With respect to a fuse of the type described above which has a wire-like fuse element and end caps on each end of the fusible element, it is desirable to provide an electrically conducting path between the end portion of the wire-like fusible element and the end cap which has a very low contact resistance.
It would be advantageous in many cases to apply an electrically conducting material to the inside of the end cap to improve electrical conduction between the fusible element and the end cap. The material, such as solder, could conveniently be heated to form a fluid and allowed to flow around the fusible element end portion in the end cap. If this were done with the type of end cap structure disclosed in the above-described U.S. Pat. No. 3,832,644, certain problems could arise.
Specifically before applying the end caps to the fuse body, a drop of liquid solder or other electrically conducting material would be deposited in end caps. Before the next step could be effected, the solder would cool and solidify. Subsequently, the end caps would be placed over the fuse body ends and heat would be applied to the end caps to remelt the solder so that it would flow around the bent over end portion of the wire-like element and form an electrically conducting connection between the end cap and the wire-like element. If the end wall of the end cap were relatively close to the fuse body end, much of the heat applied to the end cap would be conducted to the fuse body end and might partially melt or otherwise degrade the fuse body material. Further, if a relatively high-melting point solder were used, the application of heat to the end caps might cause partial melting of the bent over end portion of the wire-like element.
In any case, it would be necessary to carefully control the heating of the end cap to effect the remelting of the solder without melting or damaging the wire-like element and/or the fuse body. Consequently, it would be desirable to provide a structure for receiving a solder or electrically conducting fluid material, which structure would allow heating of the end cap to effect remelting of the fluid material without conducting or transmitting a significant portion of the applied heat to the fuse body or bent over end portion of the wire-like element.
In providing a solder-type one cap connection, appropriate cleaning and fluxing of the end cap and fuse element end portion is required in order to provide a proper solder bond of high integrity and low electrical resistance. It would be desirable to provide an end cap structure wherein a separate cleaning and fluxing operation need not be performed on the fuse wire prior to applying the end cap to the fuse body.
In providing a structure for receiving an electrically conducting fluid material for surrounding the bent over end portion of the wire-like element and for providing an electrically conducting path between the end portion and an end cap, it would also be desirable to provide a structure which prevents the electrically conducting fluid material from flowing out of the structure and alongside the exterior portion of the body of the component.